Geofísica

The Central Andes region, with significant seismic activity, has distinct faulting mechanisms across its varied topography. Notably, the sub-Andean province predominantly features reverse faulting, whereas the high Andean plateau shows a predominance of normal and strike-slip faults. Despite the importance of this extensive orogenic plateau, Bolivia remains under-documented in seismic studies.

The exponential growth of electrical resistivity tomography (ERT) methods for exploring the subsurface at large depths widened the applicability of the self-potential (SP) method, a passive geoelectrical technique suitable for a variety of purposes like mapping ore bodies or inferring fluid flow in the subsurface. Several new-generation resistivity meters have been designed to continuously log the electric potentials thus allowing for the identification of weak amplitude signals and resulting in deeper inversion models.

The crust of the South American platform recorded imprints of dynamic processes related with the opening of the Central and South Atlantic but has not been well measured. Crustal structure can be retrieved from teleseismic receiver functions using H–κ stacking, but nearly parallel stripes of high stacking values existing in stacking images for seismic stations in sedimentary area cause difficulties in identifying solutions. We show that some seemingly spurious stripes that do not point to any layer solution are helpful in the identification of the solution position.

Here we perform the integration of all available data from the BNDG (Banco Nacional de Dados Gravimétricos) and the BDEP (Banco de Dados de Exploração e Produção da Agência Brasileira de Petróleo) to provide new free-air and Bouguer gravity anomaly maps for the Brazilian territory with newly acquired data over the years, mainly in regions with no data coverage in the past. Quality controls and subsequent gridding processes, in the same system of the whole dataset, are developed on the Oasis Montaj software (OM).

Tectonic rejuvenation has been widely described in ancient rifting areas of intraplate settings, despite extensive active tectonics being discontinued long ago. Various models have been invoked to justify such tectonic rejuvenation, suggesting that the long-term deformation in intraplate interiors may be more complex than once supposed. Inherited weakness zones, e.g., pre-existing faults are stress concentrators. However, not all weakness zones in plate interiors show tectonic rejuvenation and recognizing intraplate fault reactivation remains puzzling.

We present a brief history of experimental simulations with electrokinetic potential signals observed when common porous geological media are subjected to water flow regimes. The laboratory simulations at Instituto de Astronomia, Geofísica e Ciências Atmosféricas (IAG) of the Universidade de São Paulo (USP) had to overcome several challenges over years of research work, by developing experimental design, choice of materials, and software development to guide real data interpretation and definition of acquisition procedures to be implemented in practice.

The Corumbá Group is a Neoproterozoic succession of terrigenous and carbonate sedimentary rocks located at the southern Paraguay Belt, central Brazil. The upper units of the Corumbá Group include the Ediacaran carbonate Bocaina and Tamengo formations, whose limit is characterized by polymictic breccias recognized in several sites from Corumbá to Serra da Bodoquena, Mato Grosso do Sul. Despite the widespread occurrence, the breccias are poorly described and their origin is uncertain.

Paleomagnetism is the only way to access the behavior of the geomagnetic field of internal origin through geological time. Therefore, the complete description of the paleosecular variation (PSV) is fundamental for unraveling the evolution of the Earth's core. Modeling of PSV relies on observing the fluctuations in the direction and intensity of the field on the surface, the evaluation of the paleomagnetic data dispersion in different times and situations of low and high reversal rates, the kinematics of the virtual poles during reversals, and other aspects.

This work shows the construction project of the Geophysical Test Site (Sítio Controlado de Geofísica Rasa, SCGR-I) of the Institute of Astronomy, Geophysics and Atmospheric Sciences (IAG), of the University of São Paulo (USP) and its impact on teaching and research in Geophysics. The IAG/USP test site (SCGR-I) has 1500 m², being characterized by 7 studies lines with 30 m length in the NS direction.

This paper presents an overview of the present knowledge on the Paraná magmatism and the lithospheric structure under the Paraná Basin. The genesis and diversity of the flood basalt types are linked to the structure and tectonic processes that have affected the crust and upper mantle since the Western Gondwana amalgamation until subsequent rupture.